The present invention relates to an apparatus for feeding rounded can body blanks to a welding unit which welds the longitudinal edges of the can body blanks to provide longitudinal seams.
U.S. Pat. No. 4,162,382 discloses an apparatus which employs a welding unit having an arm which extends in the direction of transport of the blanks and a rail with longitudinal grooves which guide the longitudinal edges of the blanks. A revolving transport unit, which is supported above the can body blanks, has pusher dogs that are mounted for movement about swivel axes disposed transversely to the direction of transport. The pusher dogs are oriented by a control surface on a guide track facing the transport unit. The pusher dogs are evenly distributed over the periphery of the transport unit and are provided with pusher surfaces which run perpendicular to the direction of transport. These pusher surfaces must be brought into contact with the rear ends of the can body blanks during entry into the section of the transport unit having the pusher dogs. The guide track is designed in such a way, on the side corresponding to the pusher dog section, the pusher dog surfaces temporarily retain their positions perpendicular to the direction of transport, even during their withdrawal from the pusher dog section of the transport unit.
In U.S. Pat. No. 4,162,382, the transport unit comprises two endless chains which are disposed parallel to one another. The pusher dogs are designed as levers and are disposed at a distance from one another that is less than the length of the can body blanks in the direction of transport.
For further treatment of the can body blanks it is of crucial importance that the pusher dogs of both endless chains be located in pairs opposite one another in a plane, which is aligned precisely at right angles with respect to the endless chains. Only then is it possible to weld the longitudinal edges of the can body blanks together without an offset, with the result that the front and rear ends of the can body blanks are disposed on exact perpendicular planes in relation to the longitudinal axes of the can body blanks so that the tops and bottoms can subsequently be attached tightly and without any problem. In the embodiment under discussion, the positions of the two endless chains may be affected by means of continuous adjustment of the couplings in such a way that the pusher dogs, which come in pairs, are disposed precisely opposite from one another in the region of the chain wheels. However, this does not ensure that the can body blanks in the effective region of the welding unit reach a condition in which their longitudinal edges connect without being offset longitudinally. It is not really possible to totally avoid irregularities in the distance between consecutive pusher dogs of each endless chain, due to manufacturing tolerances and/or due to various expansions during operation. Even if this type of discrepancy in distance is merely on the order of magnitude of a few tenths of a millimeter, further manufacturing operations on the welded body blanks may only be possible at an increased use of material, or the welded body blanks may even be unusable.
U.S. Pat. No. 4,774,391 proposes an apparatus which brings the endless chains that are equipped with the pusher dogs into alignment by means of adjustment templates at the point at which the front ends of the can body blanks enter the region of the welding unit. However, even in this embodiment, offsets due, for example, to wear on the endless chains or the adjustment templates, cannot be excluded. One further disadvantage which results from the use of adjustment templates is that the can body blanks can only be moved in accordance with the division of the chains. This means that it is not possible to feed the can body blanks at the desired minimal distance (preferably, one millimeter at most) into the effective range of the welding unit, so that the welding speed which the welding unit is capable of cannot be converted into the longest possible length of welding seams.